The present invention relates to a pinch roller device for pressing magnetic tape against a capstan used for a VTR or a tape recorder.
An example conventional pinch roller device is the one disclosed in the Unexamined Japanese Utility Model No. Sho62-117735. As is shown in FIG. 4, an elastic cylindrical roller 2 composed of elastic rubber is fitted over a cylindrical metal, such as brass, holder 1 wherein a small hole 1a and a large hole 1b are internally formed. A bearing 3 is fitted into the small hole 1a, and a bearing stopper sleeve 4 is fitted into the large hole 1b, so that the bearing 3 is rotatably fitted over a small diameter upper end 5a of a roller shaft 5. A swivel lever 6 supports the roller shaft 5, and additionally provided for the pinch roller device are a stopper cap 7, a washer 8 and a capstan 9, which engages a magnetic tape t.
With this arrangement, when the swivel lever 6 is swiveled in a reproduction mode, it presses the roller 2 against the capstan 9, via the magnetic tape t, so that as the capstan 9 is rotated the magnetic tape t is conveyed and information can be read from it.
In the conventional configuration, since the holder 1 is composed of a metal, such as brass, it is not deformed when the bearing 3 and the sleeve 4 are forcibly pressed into the large hole 1b. Accordingly, since the outer wall of the elastic cylindrical roller 2 that is fitted over the holder 1 is also not deformed, it uniformly contacts the magnetic tape t across its breadth, thereby facilitating the smooth and even conveyance of the magnetic tape t.
However, since an expensive metal, such as brass, is employed for the holder 1, and since to secure the roller 2 to the holder 1 an adhesive coating is applied to the outer wall of the holder 1 and the roller 2 and the holder 1 are then baked, the expenses for the material and the great amount of labor required during the manufacturing process are high, and the production costs are increased.
Thus, it has been proposed that an inexpensive, mass-produced synthetic resin be used for the holder 1. However, when simply the material of the holder 1 is changed, the following problems are encountered. As is shown in FIGS. 5 to 7, when for the holder 1, for which roller holding jaws 10 and 11 are integrally formed at the respective upper and lower ends, the outer diameters D1 and D2 of a bearing accepting portion a and a sleeve accepting portion b are set so that they correspond to the reference outer diameter D of the holder 1, while the inner diameter d of the large hole 1b is set so it is slightly smaller than the outer diameters d1 and d2 of the bearing 3 and the sleeve 4, when the bearing 3 and the sleeve 4 are forcibly pressed into and fitted in the large hole 1b, as is shown, although slightly exaggerated, in FIG. 5 the bearing accepting portion a and the sleeve accepting portion b of the holder 1 are flexibly deformed and diametrically expanded, and accordingly, a portion of the outer wall of the roller 2, which is fitted over the holder 1, is also diametrically expanded.
Since the width a of the diametrical expansion of the portion of the roller 2 is about 0.1 mm, i.e., too small to be perceived visually, the presence in the design of the expanded portion is ignored. And as a result, when the expanded portion of the roller 2 is pressed firmly against the magnetic tape t, sufficient pressure is applied to shift the tape t upward or downward and to destabilize its travel and produce noise, or to shift the magnetic tape t upward or downward so that either its upper or lower edge is forced against a guide post and damaged.
To resolve the conventional shortcomings, it is one objective of the present invention to provide an inexpensive pinch roller device that can smoothly and stably convey a magnetic tape.
To achieve this objective, according to a first aspect of the invention, a pinch roller device is provided wherein an elastic cylindrical roller is fitted over a cylindrical holder, in the inner wall of which are formed a small hole and a large hole; wherein a bearing is fitted in the large hole and a bearing stopper sleeve is pressed into the large hole, so that the bearing can be rotatably fitted over a roller shaft; wherein the elastic cylindrical holder is formed of an elastic synthetic resin; wherein the outer diameter of a sleeve accepting portion of the elastic cylindrical holder is set 0.2 mmxc2x10.05 mm smaller than the reference outer diameter of a portion other than a sleeve accepting portion and a bearing accepting portion of the elastic cylindrical holder; and wherein the outer diameter of the bearing accepting portion is set 0.1 mmxc2x10.05 mm smaller than the reference outer diameter.
According to this arrangement, since the outer diameter of the bearing accepting portion of the holder is 0.1 mmxc2x10.05 mm smaller than the reference outer diameter of the holder, when the outer diameter of the bearing is 0.1 mmxc2x10.05 mm larger than the inner diameter of the large hole of the holder, the bearing can be smoothly pressed into the large hole and the outer diameter of the bearing accepting portion of the holder can be expanded 0.1 mmxc2x10.05 mm, so as to substantially match the reference outer diameter.
Further, since the outer diameter of the sleeve accepting portion of the holder is 0.2 mmxc2x10.05 mm smaller than the reference outer diameter of the holder, when the outer diameter of the sleeve is 0.1 mmxc2x10.05 mm larger than the inner diameter of the large hole of the holder, the sleeve can be smoothly pressed into the large hole so as to support the bearing, and the outer diameter of the sleeve accepting portion of the holder can be expanded 0.2 mmxc2x10.05 mm to substantially match the reference outer diameter.
When the outer diameters of the bearing accepting portion and the sleeve accepting portion of the holder substantially match the reference outer diameter, the entire outer wall of the holder can be formed substantially planar, and accordingly, the outer wall of the elastic cylindrical roller, which is fitted over the holder, is also planar. Thus, while the entire outer wall of the roller precisely contacts the magnetic tape, the magnetic tape can be smoothly and stably conveyed without being shifted vertically, and a high quality image can be reproduced without any accompanying noise. The advantage of an inexpensive and mass produced synthetic resin holder can be obtained, and conventional shortcomings, such as the diametrically expansion of a portion of the outer wall of the roller, can be fully resolved.
According to a second aspect of the invention, a pinch roller device is provided wherein an elastic cylindrical roller is fitted over a cylindrical holder, in the inner wall of which are formed a small hole and a large hole; wherein a bearing is fitted in the large hole and a bearing stopper sleeve is pressed into the large hole, so that the bearing can be rotatably fitted over a roller shaft; wherein the elastic cylindrical holder is formed of an elastic synthetic resin; and wherein the outer diameter of a sleeve accepting portion of the elastic cylindrical holder is set smaller, by a width equivalent to the expansion produced by the insertion of the sleeve, than the reference outer diameters of a portion other than the sleeve accepting portion and a bearing accepting portion of the elastic cylindrical holder.
According to this arrangement, even when the sleeve accepting portion of the holder is expanded by forcibly inserting the sleeve into the large hole of the holder, the entire outer wall of the holder can be formed so it is substantially planar, because the outer diameter of the sleeve accepting portion is set smaller by a distance equivalent to the expansion of the diameter. Accordingly, the outer wall of the elastic cylindrical roller that is fitted over the holder is substantially planar. Therefore, while the entire outer wall of the roller securely contacts magnet tape, the magnetic tape can be smoothly and stably conveyed without being shifted vertically, so that a high quality image can be reproduced without any accompanying noise. Thus, the advantage afforded by an inexpensive and mass-produced synthetic resin holder can be achieved, and the conventional shortcoming whereof a portion of the roller is diametrically expanded can be fully resolved.
According to a third aspect of the invention, in the pinch roller device of the second aspect, the outer diameter of the sleeve accepting portion of the elastic cylindrical holder is set 0.2 mmxc2x10.05 mm smaller than the reference outer diameter of the elastic cylindrical holder.
According to this arrangement, since the outer diameter of the sleeve accepting portion of the holder is 0.2 mmxc2x10.05 mm smaller than the reference outer diameter of the holder, when the outer diameter of the sleeve is 0.1 mmxc2x10.05 mm larger than the inner diameter of the large hole of the holder, the sleeve can be smoothly pressed into the large hole so as to support the bearing, and the outer diameter of the sleeve accepting portion of the holder can be expanded 0.2 mmxc2x10.05 mm to substantially match the reference outer diameter.
According to a fourth aspect of the invention, in the pinch roller device of the second or third aspect, the outer wall of the bearing accepting portion of the elastic cylindrical holder is set smaller than the reference outer diameter of the elastic cylindrical holder a distance equivalent to the expansion due to the insertion of the bearing.
According to this arrangement, even when the bearing accepting portion of the holder is expanded by forcibly inserting the bearing into the large hole of the holder, the entire outer wall of the holder can be formed so it is substantially planar, because the outer diameter of the bearing accepting portion is set smaller by a distance equivalent to the expansion of the diameter. Accordingly, the outer wall of the elastic cylindrical roller that is fitted over the holder is substantially planar. Therefore, while the entire outer wall of the roller securely contacts magnet tape, the magnetic tape can be smoothly and stably conveyed without being shifted vertically, so that a high quality image can be reproduced without any accompanying noise. Thus, the advantage afforded by an inexpensive and mass-produced synthetic resin holder can be achieved, and the conventional shortcoming whereof a portion of the roller is diametrically expanded can be fully resolved.
According to a fifth aspect of the invention, in the pinch roller device of the fourth aspect, the outer wall of the bearing accepting portion of the holder is set 0.1 mmxc2x10.05 mm smaller than the reference outer diameter of the elastic cylindrical holder.
According to this arrangement, since the outer diameter of the bearing accepting portion of the holder is 0.1 mmxc2x10.05 mm smaller than the reference outer diameter of the holder, when the outer diameter of the bearing is 0.1 mmxc2x10.05 mm larger than the inner diameter of the large hole of the holder, the bearing can be smoothly pressed into the large hole and the outer diameter of the bearing accepting portion of the holder can be expanded 0.1 mmxc2x10.05 mm, so as to substantially match the reference outer diameter.